Telephone-exchange system



W. L. DODGE.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED AUG-7| 1918.

Patented Apr. 20,1920.

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W. L. DODGE.

TELEPHONE EXCHANGE SYSTEM.

APiPLICATlON FILED AUG-7, 1918.

1 ,337,761 Patented Apr. 20, 1920.

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UNITED STATES PATENT OFFICE.

WILLIAM L. DODGE, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO \VESTERN ELECTRIC COMPANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed August 7, 1918.

To all whom it may concern:

Be it known that I, WILLIAM L. DODGE, a citizen of the United States, residing at Maplewood, in the county of Essex, State of New Jersey, have invented certain new and useful 1m arovements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to such systems in which trunk circuits are em ployed for completing connections between telephone lines terminating at different central offices or switchboards.

The object of this invention is to provide improved signaling means for systems of this character.

In accordance with features of this invention, apparatus associated with the outgoing end of a trunk circuit operates upon the con-' nection of link circuit therewith to transmit an impulse of alternating current over the trunk circuit for operating a signal control relay at the incoming end. lVhen the connection has been set up at the incoming end. alternating current is connected with the trunk circuit at the incoming end for causing the operation of a relay at the outgoing end which effects the display of a rin ing signal. Upon the actuation of the rin ng key in the link circuit, apparatus associated with the outgoing end of the trunk circuit becomes effective to transmit an impulse of current over the trunk circuit to cause the operation of a relay in the incoming end which connects a source of ringing current with the connected extension circuit. Upon the restoration of the ring ing key to normal position, apparatus provided in the trunk circuit is rendered effective to transmit another impulse of current over the trunk circuit for releasing the ringcurrent control relay, thereby disconnecting ringing current from the connected extension circuit. Later upon the disconnection of the link circuit from the outgoingend of the trunk circuit, the apparatus there of transmits an impulse of current over the trunk circuit for causing the display of the disconnect signal.

For a more complete understanding of this invention. reference should be had to Specification of Letters Patent.

Patented Apr. 20, 1920.

Serial No. 248,760.

the following description considered in connection with the accompanying drawings, wherein Figures 1 and 2, when placed end to end with Fig. 1 to the left of Fig. 2, illustrate one embodiment of this invention.

As shown in the drawings, a trunk circuit A extends from a first to a second central ofiice. A cord circuit B located at the first central office may form part of the connection between a calling toll line D and the outgoing end of the trunk circuit A. The incoming end of the trunk circuit A may connect with the outgoing end of a toll switching trunk circuit C which extends from the second central ofIice to another switchboard which may be located in the second central ofiice or in a third central office. The incoming end of the toll switching trunk circuit C may connect directly with a local telephone line B. All apparatus shown in Fig. 1 is located at the first central office or switchboard X; that shown to the left of the dotted line 33 of Fig. 2 is located at the second switchboard Y; and that shown to the right of the dotted line 33 is located at the third switchboard Z.

The two sides of the trunk circuit A between the first and second switchboard may be simplexed for he transmission of telegraph messages thereover.

For assisting in transmitting the impulses of current over the trunk circuit, there is provided at the switchboard X, a rotary distributer shown in expanded. form in the dotted rectangle. This distributor is common to a plurality of trunk circuits, thereby making it possible to employ only one battery, preferably of fairly high voltage for furnishing impulses of direct current for transmission over the several trunk circuits served, which may be and usually are of The operator at the first switchboard X having been advised that connection is desired. between the toll line D and the line of the local subscriber E which terminates at the local switchboard Z, connection between which must be established through the switchboard Y, may communicate with the operator at the switchboard Y by means of the usual call wire circuit (not shown). The operator at the first switchboard X after having been advised by the operator at the switchboard Y that trunk circuit A is to be employed, inserts calling plug 5 of the cord circuit B into jack 6 of the trunk circuit A. Relays 7 8 and 9 there upon operate over a circuit from battery, through the lower winding of relay 7, winding of relay 8, sleeve contacts of the plug 5 and the jack 6 and the winding of relay 9 to ground. Relay 7 in operating completes parallel circuits through lamp 10 and relays 11 and 12. Relay 12 is of the quick operating and slow releasing type while relav 11 is of the slow operating type.

Relay 12 therefore operates before relay 11 and in so doing opens the energizing circuit of the relay 11 and the lamp 10. Relay 11 will not operate and the lamp 10 will not light upon the closure of the contact of relay 7. Relay 8 in operating dis connects the busy test lead from the tip contact of the plug 5 and closes through the tip talking strand of the cord circuit 13. Relay 9 in operating causes the operation of a slow release relay 13, relay 14 and a slow operating relay 15. Relay 13 in operating-opens a contact in one of the talking strands of the trunk circuit A. Relay 14 opens its normal and closes its alternate contacts, and slow operating relay 15 opens the circuit of and deenergizes slow release relay 13 and closes normally open contacts in the talking strands of the trunk circuit A. Upon the release of relay 13, the contact of the talking strand controlled thereby is closed.

lVhen the brush 19 of the distributer engages contact 25 after the operation of relay 9, relay 26 is energized over a circuit from battery through bus bar 2?, brush 19, contact 25, right-hand alternate contact of relay 9, upper normal contact and winding of relay '26, normal contact of relay 28, and the right-hand normal contact of relay 29 to ground. Relay 26 in operating establishes a locking circuit for itself through its upper alternate contact and opens its energizing circuit. Relay 26 in operating connects a source of alternating current 30 with the trunk circuit. The brushes of the distributer continue to travel and when brush 20 engages contact 31, relay 29 opertact of relay 26, contact 31, brush 20, and bus bar 32 to ground. Relay 29 in operating establishes a locking circuit for itself through its left-hand alternate contact, and opens its energizing circuit. The energization of relay 29 also opens its normal righthand contact which is in the locking circuit of relay 26, thereby causing the deenergization thereof. It will be noted therefore that relay 26 remains energized for a predetermined length of time determined by the length of time required for the brushes to travel from the contact 25 to the contact 31 of the distributor.

During the period that the relay 26 is energized, alternating current from the source 30 is connected to the trunk circuit A, thereby causing the energization of relay 35, which in operating, causes the energization of a slow release relay 36 over a circuit from battery through the upper winding and upper normal contact of relay 36 and the alternate contact of relay 35 to ground. Relay 36, upon being energized. establishes a locking circuit for itself through its middle alternate contact to ground and opens its energizing circuit. The operation of relay 36 also bridges a supervisory relay 37 across the incoming end of the trunk circuit A, and causes the lighting of a lamp 38 over a circuit from battery through the lamp 38, lower normal contact of relay 39 and the lower alternate contact of relay 36 to ground.

The operator at the switchboard Y observing the lighted condition of the lamp 38 is thereby advised that the originating operator at central office X has made connection with the proper trunk circuit and therefore may immediately insert plug 40 of the trunk circuit A into jack 41 of the toll switching trunk circuit C. Relay 42 thereupon operates, causing the energization of relay 39 which opens the circuit of and eXtinguishes the lamp 38. The energization of relay 39 also disconnects the busy test lead from the tip conductor of the plug 40, and closes a normally open contact in the tip strand of the trunk circuit A. Relay 45 in the toll switching trunk circuit C also operates over a circuit from battery through the left-hand winding of relay 45, left-hand normal contact of relay 46, upper left-hand winding of repeating coil 47, tip contacts of the jack 41 and the plug 40, upper alternate contact of relay 39, upper normal contact of ringing relay 48, retardation coil 49, upper alternate contact of relay 36, winding of relay 37, retardation coil 52, middle normal contact of ringing relay 48, ring contacts of the plug 40 and the jack 41, lower left-hand winding of the repeat ng coil 47; right-hand normal contact of relay 46, and the right-hand winding of relay 45 to ground. Relay 45 in operating causes the operation of relay 46 and the lighting of lamp 53 over a circuit from battery through the lamp 53, lower normal contact of relay 54, right-hand winding of relay 46, and the alternate contact of relay to ground. Relay 46 in operating first establishes a holding circuit for relay 45 through the lefthand winding thereof and the alternate con tact of relay 46, and then opens the original energizing circuit of relay 45, thereby preventing the operation of the supervisory relay 37 of the trunk circuit A. Relay 37 may operate momentarily, but performs no useful function at this time.

The toll switching operator at the switchboard Z observing the lighted condition of the lamp 53, knows that the connection has been built up as far as the toll switching circuit C, and having been previously advised as to the number of the desired line, inserts plug 55 of the toll switching trunk circuit G into jack 56 of the line E. Relay 54 of the toll switching trunk circuit and cut-off relay 57 thereupon operate. The operation of the former extinguishes the lamp 53 and causes the denergization of relay 46, which in releasing its armature reestablishes the original energizing circuit of relay 45 in which supervisory relay 37 is included. The supervisory relay 37 is thereby energized to cause the display of a ringing signal before the originating operator. Cutoff relay 57 in operating disconnects line relay 58 from the line.

Supervisory relay 37, upon being energized, causes the operation of a slow to operate relay 59, which opens contacts in the talking strands of the trunk circuit and connects a source of ringing current with that portion of the trunk circuit extending to the switchboard X. The closure of the middle alternate contact of relay 59 establishes a short circuit for relay 35. Relay 59 is made slow in operating so that it will not operate upon the momentary energization of relay 37. Current from the source 60 causes the operation of relay 65 at the outgoing end of the trunk circuit. Relay 65 in operating opens the energizing circuit of the slow operating and quick releasing relay 15 which thereupon releases its armatures. Upon the closure of contacts 66 of relay 15, quick operating and slow releasing relay 13 is energized to open its contact which is in the ring conductor of the trunk circuit A, thereby preventing the continued passage of alternating current to the cord circuit B. The closure of contacts 67, 68 and 69 of relay 15 connects battery through the windings of retardation coil 7 O with the talking strands of the trunk circuit Supervisory relay 71 of the cord circuit B is thereupon operated over a circuit from battery through the left-hand winding of the retardation coil 70, contacts 69 and 67 of relay 15, ring contacts of the jack 6 and the plug 5, lower normal con tact of ringing key 72, retardation coil 73, winding of supervisory relay 71, retardation coil 74, upper normal contact of ringing key 72, alternate contact of relay 8, tip contacts of the plug 5 and the jack 6 contact 68 of relay 15, and the right-hand winding of retardation coil 70 to ground. Supervisory relay 71 in operating causes the lighting of supervisory lamp 75 which now serves as a ringing signal to the origi-' nating operator.

The originating operator at the switchboard X observing the lighted condition of the lamp 75 knows that the connection has been completely set up to the line of subscriber E and that everything is in proper condition for signaling subscriber E. This originating operator may thereupon signal subscriber E by actuating ringing key 72. Ringing response relay 7'7 thereupon oper ates over a circuit from a source of ringing current 76, lower alternate contact of ringing key 72, ring contacts of the plug 5 and the jack 6, contact 67 of relay l5, condenser 78, winding of relay 77, contact 68 of relay 15, tip contacts of the jack 6 and the plug 5, alternate contact of relay 8 and the upper alternate contact of ringing key 72 to ground. The actuation of ringing key 72 also opens the circuit of supervisory relay 71, causing its deenergization and the extinguishment of the supervisory lamp 75. Relay 77 in operating causes the energiza tion of the slow release relay 28 over a circuit from battery through the left-hand alternate contact of relay 9, alternate contact of relay 77 and the winding of relay 28 to ground. lVhen the brush 19 engages contact 25 following the energization of relay 28, a slow release relay 80 is energized over a circuit from battery through the bus bar 27, brush 19, contact 25, alternate contact of relay 28, normal contact of relay 80 and the right-hand alternate contact of relay 29 to ground. Relay 80 upon being energized completes a locking circuit for itself through its left-hand alternate contact and opens its energizing circuit. Relay 80 also closes its middle and right-hand alternate contacts so that when brushes 17 and 18 next engage contacts 81 and 82 of the distribnter, relay 83 operates over a circuit from the upper terminal of battery 84 through bus bar 85. brush 17, contact 81, right-hand alternate contact of relay 14, right-hand alternate contact of relay 80, upper right-hand winding of repeating coil 86, upper left-hand winding of repeating coil 87, retardation coil 88, winding of relay 83, retardation coil 89, lower left-hand winding of repeating coil 87, lower right-hand winding of repeating coil 86, middle alternate contact of relay 80, left-hand alternate contact of relay 14,

contact 82, brush 18, bus bar 90 to the lower terminal of battery 84. Polarized relay 102 a connected in parallel with relay 83 does not operate when traversed by current of this particular polarity. The operation of relay 83 causes the energization of the slow release ringing relay 48 over a circuit from battery through the contactot relay 42, winding and lower normal contact of relay 48 and the contact of relay 83 to ground. Relay 48 upon being energized closes a locking circuit for itself which may be traced from battery through the contact of relay 42, winding and lower alternate contact of relay 48 and the normal contact of relay 35 to round, and opens its'energizing circuit. liclay 48 upon being energized first opens the tip and ring conductors of the trunk circuit A, thereby releasing supervisory relay 37, and then connects a source of ringing current 91' with the toll switching trunk circuit C. The release of supervisory relay 37 causes the deenergization of the slow release relay 59 which disconnects the source of alternating current 60 from the trunk circuit. Relay 65 thereupon releases. If the ringing key 72 is still actuated, relay 77 is energized, and the deenergization of relay 65 has no effect whatever upon any other apparatus associated with the outgoing end of the trunk circuit. However, if the ringing key 72 has been restored to normal position relay 77 is deenergized, and the release of relay 65 causes the energize,-

tion of the slow operating relay 15 which opens its normal and closes itsv alternate contacts.

Since the brushes of the distributer are rotating continuously, battery 84 is connected to the trunk circuit for but a short interval and only an impulse of current is transmitted over the trunk circuit. when the brushes leave the contacts 81 and 82, the circuit of relay 83 is opened. The

actuation of the ringing key 72 maybe for but a short interval, consequently relay 2.8 is made slow to release so that it the ringing key is released before brush 19 reaches contact 25, the alternate contact of relay 28 will of current has been transmitted over the trunk circuit, a circuit is closed through the right-hand winding of relay 29. This circuit may be traced from battery through theleft-hand alternate contact of relay 80, right-hand winding of relay 29, contact 31., brush and bus bar 82 to ground. Since the windings of the relay 29 are equal and current flows through its two windings in opposite dir ctions, that is, the windings of the relay contain equal ampere turns where- Thereiore,

by when current passes through these windings in opposite directions, equal and opposite magneto motlve forces are produced,

relay 29 releases its armatures, opening its own locking circuit and that of relay 80- which thereupon releases. If the ringing key is in its normal position and relays 77 and 28 are deenergized, when brush 19 next engages contact 25, relay 2-6 will be energized and locked up in the manner before described, connecting. the source of ringing current 30 with the trunk circuit. When the brush 2-0 next engages contact 31 after the locking up of relay'26, relay 29 is energized and locks up, releasing relay 26 in the manner before described. The connection of the source 01 ringing current 30 with the trunk circuit causes the nergization 0i relay 35 which thereupon attracts its armature, opening the locking circuit of the slow release ringing relay 48. The resulting deenergi'zation of relay 48 disconnects the source of ringing current 91 from the toll switching trunk circuit C. From this description it'will be apparent that it"the remains actuated for a relatively greater period then the actuationof the ringing key causes the transmission of an impulse of direct current over the trunk circuit to cause the energization and locking up of relay 48, and the restoration of the ringing key to normal position causes the transmission of the impulse of alternating current over the trunk circuit to cause the release of the relay 48.-

llhile the source of ringing current 91' is connected wlth the toll switching trunk aircuit C, ringing response relay 95 ofthe toll switching trunk circuit C is energized over a circuit from the source of ringing current 91 through the middle alternate contact of relay 48, ring contacts of the plug 40 and the jack 41, lower left-hand winding otthe repeating coil 17, winding ofrelay 95, condenser 96, upper left-hand winding of re peating coil 47, tip contacts of the jack 41 and the plug 40, upper alternate contact of relay 39 and upper alternate contact of relay 48 to ground. Relay 95 upon being energized causes the operation of relay 46 and a ringing relay 9'? over a circuit from bat-- tery through the left-hand winding of re lay 46, winding of ringing relay 97 and the contact of relay 95 to ground. Relay 46 in operating closes its alternate contact, thereby maintaining relay 45 energized while the original energizing circuit thereof is open at the normal contacts of relay 46 and the upper and middle normal contacts of relay 48. The ope 'ation of ringing relay 97 connects a source of ringing current 98 with the line of subscriber E for causing the operation of the usual call bell. If the subscriber E has not removed the receiver from the switchhook when the slow release ringing relay 48 releases, as before described, the release of relay 48 causes the release of relays 95, 97 and 46 and the operation of relays 45, 37 and 59. Alternating current from the source 60 is therefore again con nected with the trunk circuit, whereupon relay operates and relay 15 releases to cause the supervisory lamp 755 to light. This lamp will remain lighted until the operator at swtchboard X again actuates the ringing key 72 or until subscriber E removes the receiver from the switchhoolr, at which time it is extinguished as will more fully hereinafter appear.'

The removal of the receiver from the switchhook by subscriber E causes the operation of supervisory relay 99, which causes the energization of relay 46 over a circuit from battery through the left-hand winding of relay 46, contact of supervisory relay 99, right-hand winding of relay 46 and the alternate contact of relay 45 to ground. Relay 46 in operating first establishes at its alternate contact a circuit for maintaining relay energized and then opens at its normal contacts the original energizing circuit of relay 45. Supervisory relay 37, which is in the energizing circuit of relay 45, now releases, whereupon relays 59 and 65 release, relay 15 operates and relay 71 releases to extinguish the supervisory lamp 7 5. The talking circuit from the calling subscriber D to the called subscriber E is now completed and conversation may take place.

At the conclusion of the conversation, the subscribers restore the receivers to the switchhooks. The restoration of the receiver to the switchhook by the calling subscriber D and the operation of the generator thereat causes the energization of relay 100 which releases relay 12. Relay 11 thereupon operates over a circuit from battery through the contact of relay 7, the winding of relay 11, the contact of relay 12, and the normal contact of listening key 101 to ground. Helay 11 in operating establishes a locking circuit for itself through its own contact so that it remains energized and the lamp 10 remains lighted when the contact of relay 12 is opened upon the subsequent energization thereof due to the release of relay 100. The lighting of the lamp 10 serves as a disconnect signal from the calling subscriber.

Restoration of the receiver to the switchhook by subscriber T9 deenergizes the supervisory relay 99, whereupon relay 46 releases to again include the supervisory relay 37 in the energizing circuit of relay 45. Relay 37 now operates, closing the energizing circuit of the slow releasing relay 59, which connects the source of alternating current 60 with the trunk circuit. Relay 65 then operates, relay 15 releases and relay 13 operates. The release of relay 15 causes the energization of supervisory relay 71 which closes the circuit of and lights the supervisory lamp which now serves as a disconnect signal. Lamps 10 and 75 being lighted at the same time serve as disconnect signals to the originating operator who may disconnect the cord circuit B from the calling line D and the trunk circuit A. The disconnection from the line D causes the release of relays T and 11, whereupon the lamp 10 is extinguished. The removal of the plug 5 from the jack 6 cause the release of relay 9, whereupon relay 1 releases its armatures, closing its normal contact. When the brush 19 next engages the contact 25, slow release relay S0 is energized over a circuit from battery through the bus bar 27, brush 19, contact 25, normal contact of relay 9, normal contact of relay and the right-hand alternate contact of relay 29 to ground. He lay 80 closes its locking circuit and opens its energizing circuit, and also closes its middle and right hand alternate contacts so that when the brushes 17 and 18 engage contacts 81 and 82, an impulse of current from the battery 84 is transmitted over the trunk circuit, causing the operation of the polarized relay 102 connected in parallel with the relay 83. lVhen the brush 20 next engages contact 31, relay 29 is differentialized and releases, opening the locking circuit of relay 80 which thereupon releases. Polarized relay 102 closes its contact, estab lishing a circuit through the lower winding of relay 36. The two windings of this relay are equal and current is now flowing through them in opposite directions; consequently this relay 36 releases its armatures. The release of relay 36 causes the lighting of lamp 33 over a circuit from battery, through the lamp 38, lower alternate contact of relay 39, the lower normal contact of relay 36 to ground. The lighting of this lamp now serves as a disconnect signal. The deenergization o1 relay 36 also opens up the bridge which includes the supervisory relay 37.

The opening of the bridge containing the supervisory relay 37 causes the release of relays 59 and 65 in the trunk circuit A and the release of relay 45 in the toll switching trunk circuit C, whereupon the lamp 53 is lighted over a circuit from battery through the lamp 53, lower alternate contact of relay 54, resistance 104 and the normal contact of relay 45 to ground. The operators at switchboards Y and Z, observing the lighted condi tion of the lamps 88 and 53 respectively, may withdraw the plugs a0 and 55 from the jacks 41 and 56, whereupon all apparatus is restored to normal condition.

lVhat is claimed is:

1. A telephone exchange system compris ing a trunk circuit extendingtrom a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current and a source of dircctcurrent,means in the trunk circuit responsive to the connection of the link circuit with the trunk circuit for connecting therewith the source of alternating current and responsive to the disconnection of the link circuit from the trunk circuit for connecting therewith the source of direct current, an extension circuit at the second switchboard, a signaling device thereat, and means responsive to the connection-0f the source of alternating current with the trunk circuit for operating the signaling device and responsive to the connection of the source of direct current with the trunk circuit while connected with the extension circuit for again operating the signaling device.

2. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current and a source of direct current, means in the trunk circuit responsive to the connection of the link circuit therewith for connecting therewith one of the sources of cur rent and responsive to the disconnection of the link circuit from the trunk circuit tor connecting therewith the other source of current, an extension circuit at. the second switcl'iboard, a signaling device there-at, and means responsive to the first connection of current with the trunk eir, lit for operating the signaling device and responsive to the second connection of current with the trunk circuit while connected with the extension circuit for again operating the signaling device.

3. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current and a source Off'ClllGC'l) current, a relay in the trunk circuit responsive to the connection of the link circuit therewith for connecting the source of alternating current therewith, a second relay operating thereafter within "a predetermined period to disconnect the source of alternating current from the trunk circuit, whereby an impulse of alternating current is transmitted over the trunk circuit, a signaling device at the second switchboard, an alternating current relay thereat responsive to the impulse of alternating current, a signal control relay energized upon the response of the ringing response relay,

a signaling device operatingupon the energization of the signal control relay, an extension circuit at the second switchboard, a relay in the trunk circuit energized upon the connection of the trunk with the extension circuit for stopping the operation of the sigaling device, a relay in the trunk circuit responsive to the subsequent disconnection of the link circuit from the trunk circuit for transmitting over the trunk circuit an impulse from the source of direct current, and a relay at the second switchboard responsive to the impulse of direct current for deenergizing the signal control relay whereby the signaling device is again operated.

a. A telephone exchange system compris ing a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a source of alternating current and a source of direct current, apparatus in the trunk circuit responsiveto the connection of the link circuit therewith for transmitting an impulse of alternating current over the trunk circuit and responsive to the subsequent disconnection of the link circuit from-the trunk circuit for transmitting an impulse of direct current over the trunk circuit, an alternating current relay at the second switchboard responsive to the alternating current impulse, a relay' ing a trunk circuit extending from first to a second switchboard, a link circuit at the first switchboard, a distributer, a relay responsive to the connection of the link cir cuit with the trunk circuit, a second relay energized under the joint control of the first relay and the distributer, a third relay subsequently cooperating with the distributer to deenergize the second relay, a source of alternating current connected with the trunk circuit during the energization oi? the second relay, a fourth relay energized under the joint control of the distributor and the first relay upon the subsequent disconnection of the link circuit from the trunk circuit and subsequently deenergi-zed under the joint control of the distributer and the third relay, a source of direct current connected with the trunk circuit during the energization of the fourth relay, an alternatingeurrent relay at the second switchboard responsive to the impulse of alternating current, a direct current relay thereat responsive to the impulse of direct current, a signal control relay energized upon the response of the alternating current relay and denergized upon the response of the direct current relay, a signaling device, an operating circuit therefor completed upon the energization of the signal control relay, an extension circuit, means in the trunk circuit responsive to the connection of the trunk circuit with the extension circuit for opening the operating circuit, and a second operating circuit for the signaling device completed upon the subsequent deenergization of the signal control relay.

6. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit connected with the trunk circuit at the first switchboard, an extension circuit connected with the trunk circuit at the second switchboard, a ringing key in the link circuit, means in the trunk circuit at the first switchboard responsive to the actuation of the ringing key for transmitting an impulse of current over the trunk circuit and responsive to the subsequent restoration of the ringing key to normal position for transmitting another impulse of current over the trunk circuit, a source of ringing current at the second switchboard, and a relay in the trunk circuit controlling the connection of the source of ringing current with the ex tension circuit energized in response to the first impulse over the trunk circuit and deenergized in response to the second impulse thereover.

7. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit connected with the trunk circuit at the first switchboard, an extension'circuit connected with the trunk circuit at the second switchboard, a ringing key in the link circuit, means in the trunk circuit at the first switchboard responsive to the momentary actuation of the ringing key for transmitting two impulses of current over the trunk circuit, a source of ringing current at the second switchboard, and a relay in the trunk circuit controlling the connection of the source of ringing current with the extension circuit energized in response to the first impulse over the trunk circuit and de'elnergized in response to the second impulse thereover.

8. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit con nected with the trunk circuit at the first switchboard, an extension circuit connected with the trunk circuit at the second switchboard, a ringing key in the link circuit, a relay in the trunk circuit energized upon the actuation of the ringing key and deenergized upon the restoration thereof to normal position, a distributer, a second relay energized under the joint control of the first relay and the distributer, a third relay cooperating with the distributer for causing the subsequent de'e'nergization of the second relay, a source of direct current connected with the trunk circuit during the energization of the second relay, a fourth relay ener gized under the joint control of the distributer and the first relay when denergized and subsequently deenergized under the joint control of the distributer and the third relay, a source of alternating current connected with the trunk circuit during the energization of the fourth relay, a direct current relay at the second switchboard responsive to the impulse of direct current, an alternating current relay thereat responsive to the impulse of alternating current, a ringing relay energized upon the response of the direct current relay and deenergized upon the response of the alternating current relay, and a source of ringing current connected with the extension circuit during theenergization of the ringing relay.

9. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a relay in the trunk circuit energized upon the connectionof the link circuit with the trunk circuit and deenergized upon the disconnection of the link with the trunk circuit, a rotary distributer, a source of alternating current, a second relay operating under the joint control of the distributer and the energized first relay to transmit an impulse of current from said source over the trunk circuit, a source of direct current, a third relay operating under the joint control of the distributer and the first relay when subsequently deenergized to transmit an impulse of current from said direct current source over the trunk circuit, and a signal control relay associated with the trunk circuit at the second switchboard energized upon the transmission of the impulse of alternating current over the trunk circuit and de'e'nergized upon the transmission of the impulse of direct current thereover.

10. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit at the first switchboard, a relay in the trunk circuit energized upon the connection of the link circuit with the trunk circuit and deenergized upon the disconnection of the link with the trunk circuit, a rotary distributer, a source of alternating current, a second relay operating under the joint control of the distributer and the energized first relay to transmit an impulse of current from said source over the trunk circuit, a source of direct current, a third relay operating under the joint control of the distributor and the first relay when subsequently deenergized to transmit an impulse of current from, said direct current source over the trunk circuit,

an alternating current relay at the second switchboard responsive to the impulse of alternating current, a direct current relay responsive to the impulse of direct current, and a signal control relay energized upon the response of the alternating current relay and deenergized upon the subsequent response of the direct current relay. I

11. A telephone exchange system comprising a trunk circuit extending from a first to a second switchboard, a link circuit connected to the trunk circuit at the first switchboard, an extension circuit connected with the trunk circuit at the second switchboard,

a ringing key in the link circuit, a relay in the trunk circuit energized upon the actua tion of the ringing key and de'e'nergized upon the restoration thereof to normal position,

a rotary distributer, a source of direct current, a second relay operating under the oint control oi the dlstributer and the first relay when energized to transmit an impulse of current from said source over the trunk circuit, a source of alternating current, a third relay operating under the joint control of the distributer and the first relay when subsequently denergized to transmit .an impulse of current from said alternating current source over the trunk circuit, a ringing control relay at the second switchboard energized in response to the impulseof direct current and subsequently de'e'nergized in response to the alternating current impulse,

and a source of ringing current connected tion, a rotary distributer, a source of direct current, a second relay operating under the joint control of the distributer and the first relay when energized to transmit an impulse of current from said source over the trunk circuit, a source of alternating current, a.

third relay operating under the joint control of the distributer and the first relay when subsequently,deenergized to transmit an impulse of current from said alternating current source over the trunk circuit, adirect current relay at the second switchboard responsive to the direct current impulse, an alternating current relay at the second switchboard responsive to the alternating current impulse, a ringing control relay energized upon the response of the direct current relay and subsequentlydeenergized upon the response of the alternating current relay, and a source of ringing current connected with the extension circuit during the energization of the ringing controlrelay.

In witness whereof, I hereunto subscribe .my name this 31st day of July, A. D., 1918.

WILLIAM L. DOD GE. 

